Blood smear

BLOOD SMEARS
RAJESH MOHESS, CLT

BLOOD SMEARS
• Peripheral blood smear is a very important tool in the
hematology lab
• It provides rapid, reliable access to information about a
variety of hematologic disorders
• Examination of the peripheral blood smear is an inexpensive
but powerful diagnostic tool in both children and adults
• The smear offers a window into the functional status of the
bone marrow
• Review of the smear is an important adjunct to other clinical
data; in some cases, the peripheral smear alone is sufficient to
establish a diagnosis

BLOOD SMEARS
• An examination of the blood smear (or film) may be
requested by physicians based on medical history or
initiated by laboratory staff as part of their protocol
• Majority of cases for blood smears are from laboratory
protocol
• With the development of sophisticated automated blood-cell
analyzers, the proportion of blood-count samples that
require a blood smear has steadily diminished and in many
clinical settings is now 10 to 15 percent or less.
• Nevertheless, the blood smear remains a crucial diagnostic
aid

BLOOD SMEARS
• For a true morphological interpretation, a trained
person is required to review the smear, as automation
in hematology will normally generalize the morphology
• The indications for smear review differ according to the
age and sex of the patient, whether the request is an
initial or a subsequent one, and whether there has
been a clinically significant change from a previous
validated result (referred to as a failed delta check).
• All laboratories should have a protocol for the
examination of a laboratory-initiated blood smear

BLOOD SMEARS
• Not all hematological disorder requires a
peripheral blood smears for diagnosis.
• Some conditions can be diagnosed by other
laboratory data also.
• For example, Iron deficiency anemia can be
diagnosed by MCV, iron and ferritin levels

BLOOD SMEARS
• There are numerous valid reasons for a clinician to request
a blood smear and these differ somewhat from the reasons
why laboratory workers initiate a blood-smear examination.
• Sometimes it is possible for a definitive diagnosis to be
made from a blood smear.
• More often, the smear is an important tool in the provision
of a differential diagnosis and the indication of further
necessary tests.
• The blood smear can have an important part in the speedy
diagnosis of certain specific infections.
• Otherwise, its major roles are in the differential diagnosis
of anemia and thrombocytopenia and in the identification
and characterization of leukemia and lymphoma.

BLOOD SMEARS
Anemia:
• In patients with anemia, physician-initiated
examinations of blood smears are usually
performed in response to clinical features or to a
previously abnormal complete blood count
• Laboratory-initiated examinations of blood
smears for patients with anemia are usually the
result of a laboratory policy according to which a
blood smear is ordered whenever the
hemoglobin concentration is unexpectedly low

BLOOD SMEARS
Hemolytic Anemia:
• In the hemolytic anemias, red-cell shape is of
considerable diagnostic importance.
• Some types of hemolytic anemia yield such a
distinctive blood smear that the smear is often
sufficient for diagnosis.
• This is true of hereditary elliptocytosis, and
ovalocytosis.
• The presence of bite cells points to a Heinz body
hemolytic anemia

BLOOD SMEARS
Macrocytic Anemia:
• Patients with vitamin B12 or folic acid
deficiency, the blood smear shows
macrocytes.
• It may also show oval macrocytes and
hypersegmented neutrophils.
• When the anemia is more severe, there may
be marked poikilocytosis, with teardrop and
red-cell fragments

BLOOD SMEARS
Microcytic Anemia:
• Blood smear not very significant in diagnosis,
although very useful.
• Most common cause is iron deficiency anemia
which can be diagnosed by other blood tests
Sickle cells/Thalassemia:
• A blood smear is useful. Usually shows target
cells sickle cells

BLOOD SMEARS
Thrombocytopenia/Thrombocytosis:
• A blood smear should always be examined for
patients with thrombocytopenia.
• This is done to both confirm the
thrombocytopenia and to look for the
underlying cause.
• Falsely low platelet counts may be the result
of small clots, platelet clumping, platelet
satellitism or abnormally large platelets

BLOOD SMEARS
White Cell Disorders
(Leukemia/Lymphoma/Bone Marrow Failure):
• The precise disease classification may rely upon
evaluation of abnormal circulating cells.
• Blood smears must always be examined when
there is unexplained leukocytosis, lymphocytosis,
or monocytosis or when the flagging system of an
automated instrument suggests the presence of
blast cells
• For example, the presence of Auer rods in a blast
form in patients with acute myeloid leukemia

BLOOD SMEARS
The role of the blood smear in the diagnosis
of leukemia and lymphoma is to suggest:
• A likely diagnosis or range of diagnoses
• To indicate which additional tests should be
performed
• To provide a morphologic context without
which immunophenotyping and other
sophisticated investigations cannot be
interpreted

BLOOD SMEARS
Summary
• The blood smear remains an important diagnostic tool,
even in this age of molecular analysis
• Physicians may and should request a blood smear
when there are clinical indications for it.
• The Laboratory technologist should make and examine
a blood smear whenever the results of the CBC indicate
that a blood smear is necessary for the validation or to
further investigate an abnormality
• To avoid errors and miss any diagnoses, hematological
disorders should be investigated by both clinical data
and the peripheral smear

PREPARATION OF A BLOOD SMEAR
Principle:
• A peripheral smear may be requested by the clinician.
• It may also be performed as part of the laboratory
protocol from reflex or if there are discrepancies from
prior results.
• We will discuss the ‘Wedge Smear’
• Smears are prepared by placing a drop of blood on a
clean glass slide and spreading the drop using another
glass slide at an angle.
• The slide is then stained and observed microscopically,
mainly to determine differential count and morphology
study

Principle:
• A well-stained peripheral smear will show the red cell
background as red orange.
• White cells will appear with blue purple nuclei with red
purple granules throughout the cytoplasm.
• A well made, well distributed peripheral smear will have a
counting area at the thin portion of the wedge smear which
is approximately 200 red cells not touching.
• A good counting area is an essential ingredient in a
peripheral smear for evaluating the numbers of and types
of white cells present and evaluating red cell and platelet
morphology.

Principle:
• Functions of the peripheral blood smear are:
- provide information for diagnosis
- provide information for further testing or to
establish diagnosis
- used as a guide for therapy
- Used as an indicator to monitor the harmful
effects for chemotherapy and radiation therapy

Materials:
- Glass slides
- Applicator sticks
- Capillary tubes
- EDTA specimen (smear should be made within 4
hours of blood collection)
- Capillary blood specimen collected in
heparinized tubes

BLOOD SMEAR PROCEDURE
• Mix blood properly
• Place a small drop of blood (about 2-3 mm) about 1 cm from
the frosted end of a clean slide (slide must be completely
clean)
• Using a spreader (another slide), draw backwards into the
drop of blood (while applying pressure) – maintain an angle of
30-45 degrees

• When the spreader touches the blood, allow the
blood to spread across the edge of the spreader
• Move the spreader forward on the slide (in one
smooth motion), so a smear is made
approximately 3 to 4 cm in length.
• The smear should be half the size of the slide,
with no ridges, and a “feather edge” should be
toward the end of the smear.

• Label the frosted end of the slide with the
patient’s last name and first initial, specimen
number, and the date
• Allow the smear to air dry completely (about 5
minutes)
• Specimen can now be stained

BLOOD SMEAR
Good smear
A good smear should have the following
appearance:
• Appear smooth and uninterrupted
• Start thick and gradually thinning out (feather-edge)
• The film should take up ½ to ¾ the length of
the slide

BLOOD SMEAR LIMITATIONS
• The angle between the slides is dependent upon the size of the
blood drop and viscosity of the blood.
The optimal angle is 45 degrees
• The larger the drop of blood and lower the hematocrit, the higher
the angle needs to be so the blood smear is not too long
• Blood with a higher hematocrit needs to have a lower angle so the
smear is not too short and thick
• Glass slides must be clean; otherwise, this results in imperfect
distribution of cells and improper staining
• Smears should not be made from blood remaining on the tube
stopper as the lubricant on the stoppers can interfere with the
drying process

BLOOD SMEAR LIMITATIONS
• Once the drop of blood has contact on the slide, the smear
needs to be made immediately.
• Otherwise, the blood will clump and dry, again resulting in
uneven distribution of WBC and platelets (granulocytes will
accumulate at the edges)

POOR SMEARS
Poor smears can results from a number of
reasons, such as:
• Too large or small blood drop
• Not pushing the spreader in an even motion
• Pressing down heavily on the spreader
• Too great or small an angle of the spreader
• Speed of stroke used to move the spreader
• Clots in the blood
• Dirty (oily) slides

Blood smear

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